1. Field of the Invention
The present invention relates to a method of manufacturing a tire for vehicle wheels, of the type comprising the steps of: forming a carcass sleeve comprising a pair of annular reinforcing structures at the beads axially spaced apart from each other and at least one carcass ply having opposite end flaps each turned up at one of said annular reinforcing structures; transferring the carcass sleeve onto a shaping drum; shaping the carcass sleeve into a toroidal configuration to apply it to a belting structure at a radially inner position thereof and to a tread band circumscribing said belting structure; applying a pair of sidewalls against side surfaces of the carcass sleeve, each of said pair of sidewalls extending radially between one of the annular reinforcing structures and a side edge of the tread band.
The invention also relates to an apparatus for manufacturing a tire for vehicle wheels comprising: a building drum to form a carcass sleeve comprising a pair of annular reinforcing structures at the beads axially spaced apart from each other, and at least one carcass ply having opposite end flaps each turned up at one of said annular reinforcing structures; a shaping drum to form a tire comprising said carcass sleeve, a belting structure paired with a radially external tread band, and a pair of sidewalls applied against respective side surfaces of the carcass sleeve, each of them extending between one of said annular reinforcing structures at the beads and a side edge of the tread band, applicator devices being associated with the shaping drum to apply each sidewall to the respective side surface of the carcass sleeve; transfer devices for moving the carcass sleeve from the building drum to the shaping drum.
2. Description of the Related Art
A tire for vehicle wheels generally comprises a carcass structure having at least one carcass ply provided with respectively opposite end flaps each turned up in the form of a loop around annular reinforcing structures, each of which is usually made up of a circumferentially inextensible annular insert to which at least one filling insert is applied at a radially outer position thereof.
Associated with the carcass structure is a belting structure comprising one or more textile belt layers disposed in radial superposed relationship with respect to each other and to the carcass ply and provided with textile or metallic reinforcing cords of a respectively crossed orientation or substantially parallel to the circumferential extension direction of the tire. Applied to the belting structure, at a radially outer position thereof, is a tread band also made of elastomer material like other semifinished constituent parts of the tire.
It is to be pointed out that, to the aims of the present invention, by the term xe2x80x9celastomer materialxe2x80x9d it is intended a rubber blend in its entirety, that is the assembly made up of a base polymer suitably amalgamated with reinforcing fillers and/or process additives of various types.
Also applied to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular reinforcing structure at the beads, are respective sidewalls of elastomer material that, depending on the different embodiments, can have respective radially-external end edges either superposed on the side edges of the tread band to form a construction pattern of the type usually referred to as xe2x80x9coverlying sidewallsxe2x80x9d or interposed between the carcass structure and the side edges of the tread band, according to a construction pattern of the type referred to as xe2x80x9cunderlying sidewallsxe2x80x9d.
In most of the known processes for tire building the carcass structure and the belting structure, together with the respective tread band, are provided to be made separately from each other at respective work stations, to be subsequently mutually assembled.
More particularly, accomplishment of the carcass structure first involves that the carcass ply or plies should be laid down on a first drum, usually identified as xe2x80x9cbuilding drumxe2x80x9d, to form a cylindrical sleeve. The annular reinforcing structures at the beads are fitted or formed on the opposite end flaps of the carcass ply or plies, that are then turned up around the annular structures so as to enclose them as in a loop.
Simultaneously, on a second or auxiliary drum an outer sleeve is buildingd which is made up of the belt layers laid down in radially superposed relationship with respect to each other and to the tread band applied to the belt layers at a radially outer position. The outer sleeve is then picked up from the auxiliary drum to be transferred onto the carcass sleeve for the purpose of carrying out coupling therewith.
Assembling between the carcass sleeve and outer sleeve can be executed on the same drum used for making the carcass sleeve, in which case the concerned process is identified as xe2x80x9cone-step manufacturing processxe2x80x9d. Alternatively, assembling can be executed on a so-called shaping drum onto which the carcass sleeve and outer sleeve are transferred, to carry out tire building following a so-called xe2x80x9ctwo-step manufacturing processxe2x80x9d.
In the one-step process, application of the sidewalls takes place with the aid of the same building drum as used for formation of the carcass sleeve. The process varies depending on whether the sidewalls are first laid down on the drum or they are directly laid down on the carcass sleeve after the end flaps thereof have been turned up around the annular reinforcing structures. In the last mentioned case, in order to obtain a construction pattern of the xe2x80x9cunderlying sidewallxe2x80x9d type, each sidewall is provided to be made by laying down a strip of elastomer material on the carcass sleeve disposed in a cylindrical conformation on the drum, taking good care that the axially outer edge of the elastomer material strip should be positioned in superposed relationship with the end flap of the carcass ply already turned up around the annular reinforcing structure. The width of the elastomer material strips is such selected that the outer end flaps of the sidewalls lend themselves to be covered with the side edges of the tread band when, concurrently with an axial approaching movement of the two halves forming the drum and retaining the respective annular reinforcing structures of the carcass sleeve, said carcass sleeve is shaped into a toroidal configuration for matching with the inner surface of the outer sleeve previously placed at a centred position on the drum.
On the contrary, in order to obtain a construction pattern of the xe2x80x9coverlying sidewallxe2x80x9d type, it is preferable for the strips of elastomer material designed to make the sidewalls to be laid down on the building drum at an axially outer position with respect to the annular reinforcing structures.
The sidewall strips can be paired with the end flaps of the carcass ply so as to be turned up together with the latter, or they may stay separated from said flaps in order to enable turning up of the end flaps around the annular reinforcing structures at the beads separately from turning-up of the sidewalls, generally before shaping the carcass sleeve into a toroidal conformation.
At all events, after the carcass structure has been shaped into a toroidal configuration and matched with the outer sleeve, appropriate expandible portions of the building drum, consisting of a system of levers or of inflatable bags for example, cause overturning of the strips of elastomer material in order to apply them against the side surfaces of the carcass structure.
Methods and apparatuses operating in accordance with the above-mentioned principles are described in documents FRA-2.093.180 and U.S. Pat. No. 3,990,931, for example.
Referring now to the two-step manufacturing processes, the construction pattern of the xe2x80x9cunderlying sidewallxe2x80x9d type is obtained by laying down the elastomer material strips on the carcass sleeve in the same manner as above described with reference to the one-step manufacturing process.
In fact, the sidewalls are arranged on the carcass sleeve formed into a cylindrical conformation on the building drum, which in this case can be also called xe2x80x9cfirst-step drumxe2x80x9d, to join the respective end flaps to the side edges of the tread band, concurrently with the step of shaping the carcass sleeve on the shaping drum, also referred to as xe2x80x9csecond-step drumxe2x80x9d.
The construction pattern of the xe2x80x9coverlying sidewallxe2x80x9d type can be obtained by applying the elastomer material strips designed to form the sidewalls directly on the carcass sleeve, as provided for the above-described corresponding pattern of the xe2x80x9cunderlying sidewallxe2x80x9d type, while at the same type adopting particular expedients, such as use of strips of adhesion-preventing material for example, in order to make the elastomer strips fixedly adhere to the carcass ply only and exclusively close to the annular reinforcing structures.
After the carcass sleeve has been transferred to the shaping drum, each of the elastomer material strips is, by a manual action and/or with the aid of appropriate devices, radially and axially spread apart outwardly with respect to the sleeve, to enable removal of the adhesion-preventing films. Then shaping of the carcass into a toroidal conformation is carried out in order to match it with the outer sleeve previously placed at a centred position on the carcass sleeve itself. Subsequently, the spread-apart sidewalls are overturned with the aid of rolling devices or devices of other types, to be applied against the side surfaces of the carcass structure and the tread band.
In document EP-A-822059 an apparatus and a method are disclosed which enable the above described operations to be carried out without requiring application of adhesion-preventing films.
In document U.S. Pat. No. 5,380,384 the shaping step for application of the outer sleeve to the carcass sleeve is provided to be carried out on the first-step drum whereas the second-step drum is exclusively intended for carrying out all operations aiming at applying the sidewalls, in accordance with the construction pattern of the xe2x80x9coverlying sidewallxe2x80x9d type.
In an attempt to optimize distribution of the floor to floor times between the first and second steps in a two-step manufacturing process, in document EP 997.263 a proposal has been made to carry out application of the outer sleeve and subsequent application of the sidewalls completely on the shaping drum.
In accordance with the present invention, it has been found that by carrying out the processing steps aiming at applying the sidewalls on two separate drums, subsequently to the working operations on the building drum, optimisation of the floor to floor times can be further improved while at the same time surprising economical advantages are achieved, as a result of simplification of the machinery and the operating flexibility of same in connection with building of tires of different typologies and/or sizes.
In more detail, the invention relates to a method of manufacturing a tire for vehicle wheels, characterized in that before transferring the carcass sleeve to the shaping drum, the following steps are carried out: positioning said sidewalls on an intermediate drum, which sidewalls have respective inner end flaps facing each other and mutually spaced apart; transferring the carcass sleeve onto the intermediate drum; engaging the inner end flap of each sidewall against said carcass drum at one of the annular reinforcing structures at the beads.
More specifically, positioning of each sidewall comprises the step of winding up a strip of elastomer material around a first radially expandible portion of the intermediate drum.
Following said transferring step, the carcass sleeve is advantageously coaxially positioned around the intermediate drum with the annular reinforcing structures at the beads that are each disposed close to the inner end flap of one of said sidewalls.
The engagement step of the inner end flap of each sidewall is preferably carried out by radial expansion of the sidewalls placed on the intermediate drum.
It may be also advantageously provided that following radial expansion of the sidewalls, an end section of the inner end flap of each sidewall will be submitted to an additional radial expansion step and applied against an axially inner shoulder defined by the respective annular reinforcing portion at the bead.
In a preferential embodiment of the subject method, before or during radial expansion of the sidewalls, an axial tensioning step of the carcass sleeve is provided to be carried out.
In more detail, axial tensioning of the carcass sleeve is preferably accomplished by bringing pusher elements in thrust relationship with axially inner shoulders defined by the annular reinforcing portions at the beads.
Furthermore, the pusher elements are preferably caused to be axially moved apart from said axially inner shoulders before carrying out the additional radial expansion of said end sections.
In a first embodiment, said additional radial expansion is carried out as a continuation of the radial expansion of the sidewalls: alternatively, said additional radial expansion is carried out after completion of the tire by shaping of the carcass and application of the outer sleeve and the sidewalls, both in the overlying sidewall pattern and in the underlying sidewall pattern, as above described.
This second embodiment offers a high degree of security in maintaining the carcass centring during the operations for tire completion and facilitates subsequent moving away of the pusher elements, that are no longer constrained by the belting action exerted by the cylindrical carcass sleeve.
In a preferential embodiment the following steps are also provided: forming an outer sleeve comprising the belting structure and the tread band applied to the belting structure at a radially outer position thereof; placing the outer sleeve at a centred position around the carcass sleeve previously transferred onto the shaping drum, before terminating the shaping step.
According to a possible alternative embodiment, application of the sidewalls against the side surfaces of the carcass sleeve can be carried out before completing the shaping step.
It is a further object of the present invention to provide an apparatus for manufacturing tires for vehicle wheels, characterized in that it further comprises: an intermediate drum arranged for engagement of the carcass sleeve carried by said transfer devices; an auxiliary unit to position said sidewalls on the intermediate drum, said sidewalls having respective inner end flaps facing each other and mutually spaced apart; said intermediate drum comprising engagement devices to cause engagement of the inner end flap of each sidewall against said carcass sleeve, at one of the annular reinforcing structures at the beads.
Preferably, said engagement devices comprise first radially expandible portions of the intermediate drum.
Advantageously, these first radially expandable portions define respective rest seatings for the sidewalls positioned on the intermediate drum.
It is further preferably provided that said engagement devices should comprise auxiliary expandible portions located at axially inner positions with respect to the first radially expandible portions and movable between a rest condition in which they are substantially in radial alignment with the first expandible portions themselves, and an operating condition in which they radially project from the first radially expandible portions.
Each of said auxiliary radially expandible portions advantageously offers a rest seating for the inner end flap of one of said sidewalls.
It is also provided that in the operating condition, each of said auxiliary radially expandible portions should have one axially outer surface thereof in abutment relationship with an axially inner shoulder defined by one of said annular reinforcing portions at the bead, to apply the inner end flap of the respective sidewall against the shoulder itself.
Preferably, the intermediate drum further comprises pusher elements axially movable between a rest position which is axially internal with respect to the inner end flaps of the sidewalls disposed on the intermediate drum, and an operating position in which said pusher elements are radially superposed with respect to the inner end flaps of the sidewalls.
In more detail, said pusher elements in the operating position act against axially inner shoulders defined by said annular reinforcing portions at the bead, to give rise to an axial tensioning of the carcass sleeve engaged on the intermediate drum.
In a preferential embodiment, said applicator devices comprise radially expandible diaphragm elements arranged to supply rest seatings for the sidewalls carried by the carcass sleeve transferred to the shaping drum.
It is also preferably provided that said transfer devices should comprise a first transferring member to move the carcass sleeve from the building drum to the intermediate drum and a second transferring member to move the carcass sleeve together with the sidewalls associated therewith from the intermediate drum to the shaping drum.